Air valve carburetor

ABSTRACT

In an air valve carburetor, an adjustable idle mixture stop operatively connected to the air valve engages an arm extending from the fast idle cam. For cold start enrichment, the arm is moved out from under the idle stop to close the air valve; this increases the fuel metering signal in the metering zone between the air valve and the throttle and thus the fuel flow thereto. To overcome friction between the idle mixture stop and the arm, a canted leaf spring attached to the throttle lever engages a pin extending from the cam. As the throttle is opened, the spring moves the cam to kick the arm out from under the idle mixture stop.

United States Patent Gural June 3, 1975 AIR VALVE CARBURETOR Primary ExaminerTim R. Miles [75] Inventor: John Gun" pinsford Assistant ExaminerWilliam Cuchlinski, Jr.

Attorney, Agent, or Firm-C. K. Veenstra [73] Assignee: General Motors Corporation,

Detroit, Mich. 221 Filed: Feb. 4, 1974 {57] ABSTRACT 2 AppL 439,286 In an air valve carburetor, an adjustable idle mixture stop operatively connected to the air valve engages an arm extending from the fast idle cam. For cold start UaS- Cl. t enrichment the arm is moved out from unde the Cl. top to lo e the air valve; increases thg fuel me- Fleld Of Search A, te -ing ignal in the metering zone between the air valve and the throttle and thus the fuel flow thereto. [56] Referemes cued To overcome friction between the idle mixture stop UNITED STATES PATENTS and the arm, a canted leaf spring attached to the 3,023,744 3/1962 Mick 261/50 A UX throttle lever engages a P extending from the 3,043,572 7/1962 Ott et a1 261/52 X As the throttle is opened, the spring moves the cam to 3,342,462 9/1967 Mick 261/50 A X kick the arm out from under the idle mixture stop. 3,841,281 l0/l974 Mick 261/50 A X 3 Claims, 6 Drawing Figures AIR VALVE CARBURETOR This invention relates to an air valve carburetor for internal combustion engines and, more particularly, to an air valve carburetor having a fast idle cam and an arm extending therefrom which engages an adjustable stop (which holds the air valve open) for controlling the idle mixture. Means are described which disengages the stop from the arm when the throttle is opened to allow the air valve to close for cranking enrichment.

As described in U.S. Pat. No. 3,023,744 Mick, an example of mechanical linkage for positioning the air valve included a fast idle cam which engages a cam follower for limiting throttle closure and positioned by a thermostat responsive to engine temperature, a lever connected to the air valve shaft and having an adjustable idle stop member which engages a contoured portion of the cam, and a spring biasing the air valve closed. When the engine is cold, the cam is repositioned by the thermostat to allow the air valve to be completely closed to provide a maximum metering signal to the fuel supply means, thereby maximizing fuel flow for cold start enrichment.

However, it is possible that mechanical friction between the fast idle cam and the air valve lever and/or between the throttle cam follower and the cam may prevent the air valve from closing as desired. To ensure closure of the air valve for cold starts, the novel linkage set forth in the present invention repositions the fast idle cam when the throttle is opened and the arm supports the adjustable idle stop. This allows the air valve lever, which carries the adjustable idle stop, to disengage the arm and move, thereby closing the air valve to provide cold start enrichment.

In the preferred embodiment a canted, resilient leaf spring has a flat portion at one end which is secured to the auxiliary throttle lever and has a bent portion at the other end which is disposed in the rotative path of the cam and further has a leading edge which engages a pin on the fast idle cam when the throttle is opened and the arm engages the idle stop. In so doing, the leading edge of the spring moves the cam and kicks the arm thereof out from under the air valve lever to allow the air valve to close. However, the construction of the bent portion and the disposition of the leading edge in the rotative path of the pin allows the opposite edge of the spring to slide over the pin when the throttle is closed. Accordingly, this allows the canted spring to engage the pin in a manner henceforth referred to as a unidirectional ratcheting manner during throttle movement. The ratcheting movement ensures that the position of the fast idle cam is not reset as the throttle closes so that the cam may move under the influence of the thermostat during normal warm-up to limit closing of the throttle in a conventional manner.

It is a principal object of the present invention to set forth means for releasing the air valve from the influence of the temperature-controlled cam in order to enrich the cranking mixture in a carburetor having an air valve controlled fuel metering system.

It is a further object of this invention to set forth means for releasing the air valve from under the influence of the temperature controlled cam to allow the air valve to close to increase the metering signal to means for supplying fuel to an air valve carburetor for delivery to an engine in order to obtain cranking enrichment.

Still another object of this invention is to disclose an air valve carburetor having novel means for releasing the air valve idle mixture adjusting screw from under the arm extending from the fast idle cam only when the throttle is opened and the arm supports the screw, in order to close the air valve thereby increasing the metering signal to means for supplying fuel to the carburetor to increase fuel flow to the engine for cranking enrichment.

The details as well as other objects and advantages of this invention are set forth in the remainder of the specification and are shown in the drawings in which:

FIG. 1 is a sectional elevational view of the carburetor showing the basic metering linkage and further showing the controls responsive to ambient air pressure and temperature and manifold vacuum;

FIG. 2 is a side elevational view of the carburetor with parts broken away to illustrate the linkage responsive to engine operating temperatures and showing the linkage in a position as required for a hot start and the spring for releasing the fast idle cam to close the air valve;

FIG. 3 is a view similar to FIG. 2 with the linkage positioned as required for a cold start;

FIG. 4 is a view of the FIG. 2 linkage, enlarged to illustrate further details of the means for releasing the fast idle cam to allow closing of the air valve;

FIG. 5 is an end elevational view of the FIG. 4 linkage taken in the direction indicated by the arrows 55 of FIG. 4; and

FIG. 6 is a sectional view taken along line 66 of FIG. 4, showing the canted configuration of the fast idle cam release spring.

Referring first to FIG. I, the carburetor 10 has a mixture conduit 12 including the air inlet 14 and a mixture outlet 16 which discharges to the engine. A throttle 18 is rotatably disposed in mixture outlet 16 on a throttle shaft 20.

An air valve 22 is rotatably disposed in air inlet 14 on an air valve shaft 24. A spring 26 is secured to the downstream edge 28 of air valve 22 and extends to a bracket 30 to bias air valve 22 to the closed position shown.

A tab 32 reaches upwardly from air valve 22 and is connected by a link 34 to a diaphragm 36. A chamber 38, formed between the right side of diaphragm 36 and a cover member 40, is connected by a tube 42 to a region 44 of mixture conduit 12 defined between air valve 22 and throttle 18.

A chamber 46 defined between the left side of diaphragm 36 and a cover member 48 is subjected to substantially atmospheric pressure, present in air inlet 14 and in the air cleaner (not shown) through openings such as 50, S2 and 54. (The air cleaner seats on a rim 56 disposed about the upper portion of carburetor 10).

In operation, chamber 38 is subjected to the subatmospheric pressure created in region 44 as throttle 18 is opened, and diaphragm 36 acts through link 34 to pull air valve 22 clockwise toward its open position. Spring 26 is effective to balance the opening force of diaphragm 36, thereby creating a substantially constant subatmospheric pressure in region 44. By thus establishing a constant pressure drop across air valve 22, the area about and thus the rotative position of air valve 22 is determined by and is a measure of the rate of air flow through mixture conduit 12.

A tab 58 extends upwardly from air valve 22 and is connected through a link 60 to one end 62 of a lever 64. The opposite end 66 of lever 64 is pivoted about a pivot pin 68. intermediate ends 62 and 66, a hanger 70 descends from lever 64 into a carburetor fuel bowl 72 disposed therebelow. The lower end 74 of hanger 70 has a hook 76 which is received in a recess 78 formed in a metering rod 80.

It may be noted that hanger 70 extends through an opening 82 in a cover 84 for fuel bowl 72. Opening 82 is covered by a slider 86 which shifts horizontally dur ing movement of hanger 70.

Metering rod 80 is disposed in a fuel passage 88 having its lower end 90 disposed to receive fuel from a well 92 formed in the bottom of fuel bowl 72. The upper end 94 of fuel passage 88 has an opening 96 through which fuel is discharged into region 44 of mixture conduit 12. It will be appreciated. therefore, that the fuel in fuel bowl 72 is subjected to a substantially constant metering head from the substantially atmospheric pressure in the upper portion of the fuel bowl to the generally constant subatmospheric pressure in region 44 of carburetor 10.

A metering jet or orifice plate 98 is disposed in fuel passage 88 around the tip 99 of metering rod 80. Metering rod 80 has flat tapered surfaces 100 on opposite sides which, upon reciprocation of metering rod 80 in jet 98, vary the area available for fuel flow through jet 98.

In operation, as air valve 22 opens by clockwise rotation, link 60 rotates lever 64 in a clockwise direction. Lever 64 then lifts hanger 70 to move the metering rod 80 generally upwardly and rightwardly in fuel passage 88. Thus as air valve 22 is opened to increase the area available for air flow through air inlet 14, metering rod 80 is shifted to increase the area available for fuel flow through metering orifice 98. By this means, a substantially constant air-fuel ratio may be maintained the precise proportion being controlled by the geometry of tapered surfaces 100 and of the linkage between air valve 22 and metering rod 80.

A spring 102 extends from an annular ledge 104 formed in fuel passage 88 to the lower end 106 of metering rod 80 to take up any slack in the linkage and to load metering rod 80 against jet 98.

A slot 108 is formed in the end 62 of lever 64. Link 60 is connected to lever 64 by having one end 110 disposed in slot 108. A link 112 extends from end 110 to an arm 114 of a supplementary lever 116 pivoted at a pin 118. The opposite arm 120 of the lever 116 is connected by a link 122 to one end 124 of an aneroid or bellows 126. The opposite end 128 of aneroid 126 is connected to a reciprocable plunger 130 threadably received by an adjusting screw 132, guided in the bore 134 of an adjustable stop 136, and extending to a diaphragm 138.

A chamber 140 defined between the right side of diaphragm 138 and a cover member 142 is subjected to the manifold vacuum in mixture outlet 16 downstream of throttle 18, while a chamber 144 defined between the left side of diaphragm 138 and a cover member 146 is subjected to substantially atmospheric pressure. The resulting rightward bias on diaphragm 138 is resisted by a spring 148 disposed between the head 149 of adjusting screw 132 and a support 150. The linkage is shown in the position assumed when manifold vacuum is sufficient to overcome the force of spring 148.

When throttle 18 is opened and manifold vacuum drops to a point indicative of the need for an enriched air-fuel ratio, spring 148 moves adjusting screw 132 leftwardly until head 149 abuts adjustable stop 136. Plunger 130 is thus moved leftwardly, and a spring 151, extending between end of supplementary lever 116 and a support 152, moves supplementary lever 116 counterclockwise to move link 122 and aneroid 126 leftwardly. Link 112 is then pulled downwardly to reposition end 110 of link 60 in slot 108, thereby resulting in a shorter lever arm defined between end 110 of link 60 and pivot pin 68. This increases the travel of metering rod 80 through metering jet 98 for equivalent opening movement of air valve 22 to provide an enriched air-fuel mixture.

When manifold vacuum increases to a point indica tive of a need for a leaner air-fuel ratio. diaphragm 138 forces link and adjusting screw 132 rightwardly until an end 154 of adjusting screw 132 engages support 150. This forces aneroid 126 and link 122 rightwardly, resulting in clockwise rotation of lever 116. Link 112 then raises the end 110 of link 60 in slot 108 to increase the lever arm defined between link end 110 and pivot pin 68. This reduces the travel of metering rod 80 through metering jet 98 for equivalent opening movement of air valve 22 to provide a leaner air-fuel mixture.

Upon a decrease in ambient air pressure or an increase in ambient air temperature, both indicative of a reduction in air density and consequently a reduction in the mass rate of air flow through air inlet 14 for equivalent volume air flow, aneroid 126 expands, forcing link 122 rightwardly and causing clockwise rotation of lever 116. Link 122 then raises the end 110 of link 60 in slot 108 to increase the lever arm defined between link end 110 and pivot pin 68. The increased lever arm reduces the travel of metering rod 80 in metering jet 98 for equivalent movement of air valve 22 to prevent air-fuel mixture enrichment caused by a reduction in air density.

Upon an increase in ambient air pressure or a decrease in ambient air temperature, both indicative of an increase in air density, aneroid 126 contracts. Spring 151 then causes counterclockwise movement of supplementary lever l 16, and link 112 then moves link end 110 downwardly in slot 108 to shorten the lever arm defined between end 110 and pivot pin 68. The shortened lever arm increases the travel of metering rod 80 in jet 98 for equivalent movement of air valve 22 to prevent leaning of the air-fuel mixture due to an increase in air density.

Referring now to FIGS. 2 and 3, a housing 156 encloses a thermostat 158 subjected to engine operating temperatures for example, by passing air in heat exchange relationship with engine exhaust gases and then through housing 156. Thermostat 158 positions a shaft 160 to which a thermostat lever 162 is secured. A link 164 extends from thermostat lever 162 to an intermediate lever 166 pivotally mounted about a cold enrichment shaft 168. It is well to point out that thermostat lever 162 is shown in FIG. 2 in a position corresponding to a hot start, with counterclockwise rotation of lever 162 corresponding to cooling of the engine.

A vacuum break lever 170 is secured to cold enrichment shaft 168 and has a tang 172 engaged by an arm 174 of lever 166. A link 176 extends from vacuum break lever 170 and is received in a slot 178 formed in the plunger 180 of a vacuum break unit 182.

Vacuum break unit 182 includes a diaphragm 184 biased toward the position shown by a spring 186. The

vacuum chamber 188, defined between the right side of diaphragm 184 and a cover member 190, is subjected to the manifold vacuum in mixture outlet 16 downstream of throttle 18. A chamber 192, defined between the left side of diaphragm 184 and a cover member 194, is subjected to atmospheric pressure. As soon as the engine starts, or after a suitable time delay provided by conventional time delay units, diaphragm 184 is pulled rightwardly against the bias of spring 186. A washer 196, secured to diaphragm 184, then pulls a cup member 198 toward the right. This compresses a spring 200 to pull plunger 180 toward the right. Link 176 is thus moved rightwardly to rotate vacuum break lever 170 and cold enrichment shaft 168 in a clockwise direction the degree of rotation being limited by abutment of tang 172 with arm 174 when the force exerted by spring 200 is balanced by the force exerted by thermostat 158. The resulting counterclockwise movement of a cold enrichment lever 202, shown in FIG. 1 and secured to cold enrichment shaft 168, carries pivot pin 68 extending therefrom and thus moves lever 64 to increase the lever arm defined between link end 110 and pivot pin 68. This reduces travel of metering rod 80 in jet 98 for equivalent movement of air valve 22 and thus leans the air-fuel mixture after the engine starts.

As thermostat 158 is thereafter warmed during engine operation, thermostat lever 162 is rotated clockwise as viewed in FIG. 3 to the position shown in FIG. 2 corresponding to a warm engine. Lever 162 then acts through link 164 to rotate intermediate lever 166 clockwise as viewed in FIG. 3 to the position shown in FIG. 2. This permits further clockwise rotation of vacuum break lever 170 and cold enrichment shaft 168 under the force imparted by vacuum break unit 182 which thus imparts counterclockwise rotation to a cold enrichment lever 202 as viewed in FIGv 1. The resulting counterclockwise movement of pin 68 carried by cold enrichment lever 202 on enrichment shaft 68 moves lever 64 with respect to link 60 and thus increases the lever arm defined between link end 110 and pivot pin 68. This increase in the lever arm reduces the travel of metering rod 80 in jet 98 for equivalent movement of air valve 22 to lean the air-fuel mixture as the engine warms. This will continue as the engine warms until a tang 204 on vacuum break lever 170 engages an adjustable stop 206 as shown in FIG. 2.

As thermostat 158 cools after engine operation, thermostat lever 162 is rotated counterclockwise from the position shown in FIG. 2 to that shown in FIG. 3. Lever 162 then acts through link 164 to rotate intermediate lever 166 counterclockwise as viewed in FIGS. 2-3. At a selected temperature, arm 174 on lever 166 engages tang 172 on vacuum break lever 170 to move lever 170, and thus cold enrichment shaft 168, counterclockwise away from stop 206. This imparts clockwise rota tion to cold enrichment lever 202 as viewed in FIG. 1, and the resulting clockwise movement of pivot pin 68 shifts lever 64. As lever 64 is shifted. metering rod 80 is raised to provide increased fuel flow for cold start. In addition, the lever arm defined between link end 110 and pivot pin 68 is decreased to provide increased travel of metering rod 80 in jet 98 for equivalent movement of air valve 22 and thus provide an enriched airfuel mixture for cold operation.

Referring now to FIGS. 2 through 6, a link 208 extends from intermediate lever 166 and is received in an arcuate slot 210 of a fast idle cam member 212 pivoted on the carburetor by means of a pin 213. Fast idle cam member 212 has a series of steps 214 or alternatively a smoothly contoured surface abutted by a cam follower tang 215 which extends from a fast idle lever 216 pivoted on throttle shaft 20.

A fast idle adjusting screw 217 is threadedly carried by a tang 218 of fast idle lever 216. Screw 217 abuts a rounded end 222 of an abutment arm 224 extending from an auxiliary throttle lever 226 secured to throttle shaft 20. The function of fast idle adjusting screw 217 is to allow adjustment of the amount of throttle opening during engine idling, in order to limit the idle speed. Adjustment is provided by turning screw 217 which re positions lever 226, throttle shaft 20 and throttle 18 in relation to the fast idle lever 216 which, through follower tang 215, engages and is limited by fast idle cam 212.

A link 228 extends from throttle lever 226 and is re ceived in an arcuate slot 230 of an air valve lever 232 secured to air valve shaft 24. A tang 234 on air valve lever 232 carries an idle mixture adjusting screw 236 which engages an arm 238 extending from fast idle cam 212. The function of idle mixture adjusting screw 236 is to allow adjustment of the amount of air valve opening when the throttle is closed and the engine is idling. This determines the vacuum in the metering zone 44 which in turn establishes the amount of fuel flow thereto. Adjustment is provided by turning screw 236 when it engages arm 238 of cam 212, whereby air valve lever 232, shaft 24 and air valve 22 are moved in relation thereto. For example, as screw 236 is turned it moves tang 234 from arm 238 and thereby rotates lever 232, shaft 24 and air valve 22 counterclockwise. This opens the air valve and reduces the vacuum in the metering zone 44 therebelow thereby reducing the amount offuel flow thereto to lean the idle mixture. A]- ternatively, if screw 236 is backed off from arm 238 it allows air valve 22 to close thereby increasing the metering signal to increase fuel flow and richen the idle mixture.

Link 228 is provided so that as auxiliary throttle lever 226 is rotated counterclockwise as throttle 18 approaches a wide open throttle position, link 228 is pulled downwardly to provide counterclockwise rotation of air valve lever 232 and air valve shaft 24 to assist in opening air valve 22. When needed to unload a flooded engine, throttle 18 can be opened completely, This rotates lever 226 counterclockwise and link 228 then opens air valve 22 partially so that little, if any, vacuum is produced in region 44 and fuel flow is minimized thereby.

Auxiliary throttle lever 226 is urged in the clockwise or throttle closing direction by a torsion return spring 240 loosely wound around throttle shaft 20 and engag ing both throttle lever 226 and an ear 242 on fast idle lever 216. Spring 240 imparts counterclockwise torsion to fast idle lever 216 and clockwise torsion to auxiliary throttle lever 226 to ensure that fast idle adjusting screw 217 will engage arm 224 of auxiliary throttle lever 226.

Stop car 242 of fast idle lever 216 abuts a fast idle lever stop 244 cast in carburetor 10 to limit the counterclockwise movement of fast idle lever 216.

As best shown in FIGS. 4 and 5, a fast idle cam weight 252 is secured by a ratchet pin 250 to fast idle cam 212. The weight 252 gravitationally biases the fast 7 idle cam 212 counterclockwise to the upright position shown in FIGS. 2 and 4.

As thermostat 158 is warmed during engine operation, thermostat lever 162 and link 164 pull intermediate lever 166 in a clockwise direction, as viewed in FIGS. 23. This pushes link 208 downwardly and leftwardly to permit counterclockwise movement of fast idle cam member 212, under the bias of weight 252, from the FIG. 3 position toward the FIG. 2 position. Cam follower tang 215 may then engage the lower step 214 on fast idle cam member 212, permitting further movement of lever 216, auxiliary throttle lever 226, and throttle shaft to allow throttle 18 to close to reduce engine idle speed.

As shown in FIG. 2, when the engine is hot thermostat 158 positions thermostat lever 162, link 164, intermediate lever 166, link 208, and fast idle cam member 212 so that arm 238 on cam 212 is engaged by idle mixture adjusting screw 236. This limits movement of air valve lever 232 and air valve shaft 24 in the clockwise or air valve closing direction to prevent an overly rich idling air-fuel mixture.

As the engine temperature decreases after the engine stops, thermostat 158 rotates thermostat lever 162 counterclockwise to lift link 164 and rotate intermediate lever 166 counterclockwise. Link 208 is then pulled upwardly and rightwardly to attempt to rotate fast idle cam member 212 clockwise. If this happens cam follower tang 215 on fast idle lever 216 is then received on the high step 214 of fast idle cam 212 to limit clockwise movement in the throttle closing direction of fast idle lever 216, auxiliary throttle lever 226 and throttle shaft 20. Also, as cam 212 rotates clockwise to a cold position screw 236 will disengage arm 238 to enrich the cold start idle mixture by allowing the air valve to fully close thereby increasing the metering signal in metering zone 44. However, mechanical friction may be sufficient to prevent thermostat 158 from resetting the linkage and allowing air valve 22 to close. That is, fric tion may preclude sliding between arm 238 and idle mixture adjustment screw 236.

To preclude this so that the air valve may fully close for cold start enrichment a novel means for releasing the arm from under the idle mixture adjusting screw is provided. The release means comprises a canted spring 246 having a flat portion 247 attached to auxiliary throttle lever 226. The canted configuration of spring 246 is best shown in FIG. 6, where it can be seen that the spring further has a bent portion 248 obliquely canted from flat portion 247. Bent portion 248 has a leading edge 249 which is disposed in the rotative path of pin 250 secured to cam 212. It should be noted that edge 249 is the leading edge when lever 226 moves as the throttle is opened. Pin 250 extends perpendicularly and outwardly from the plane of rotation of fast idle cam 212 and is adapted for registration with bent portion 248 and edge 249 so that the spring and pin coact in a unidirectional ratcheting manner in the throttle opening direction edge 249 engages pin 250 but in the throttle closing direction bent portion 248 rides or snaps over pin 250.

In operation, when arm 238 supportingly engages adjustment screw 236 to hold the air valve open thus preventing the desired manner of cold start enrichment, throttle lever 226 may be moved counterclockwise as the throttle is opened to move spring 246 into the rotative path of pin 250. As spring 246 moves counter' clockwise leading edge 249 engages pin 250 as shown in FIG. 4 to move the pin and cam 212 clockwise. This repositions arm 238 from under idle mixture adjusting screw 236 to allow it and tang 234 to drop within a recessed notch portion 251 of arm 238. Accordingly, air valve lever 232, shaft 24 and air valve 22 rotate clockwise under the bias of air valve spring 26 thereby closing the air valve for subsequent cold start enrichment.

However, as auxiliary throttle lever 226 is rotated in a clockwise direction as the throttle closes, bent portion 248 of spring 246 slides or snaps over pin 250 in a unidirectional ratcheting manner without resetting the fast idle cam position. This allows cam 212 to be positioned by thermostat 158 in a conventional manner. Thus, it can be seen that the release means do not affect the conventional operation of fast idle cam 212.

It should be noted that link 208 normally abuts the upper end 254 of arcuate slot 210 in fast idle cam 212 to position the cam. Counterweight 252 rotates cam 212 counterclockwise to the extent permitted by link 208 and slot 210. Counterweight 252 and link 208 thereby coact to establish the position of the cam. At a selected temperature, arm 238 is positioned under idle mixture adjustment screw 236. This occurs when cam 212 is near the position shown in FIGS. 2 and 4 and arm 238 is near the zenith of its arc whereby air valve 22 is then held slightly open in order to lean the idling mixture after the engine warms.

It is important to note that as the air valve is allowed to close beyond the idle position established by screw 236 and arm 238, this repositions metering rod in orifice 98 to restrict fuel flow therethrough, which would in and of itself not achieve the desired effect of cold start enrichment. However, this fuel flow restriction is more than compensated by the greatly reduced (subatmospheric) pressure which is obtained in region 44 as the air valve is allowed to close beyond its idle position. The increased metering signal achieved by closing the air valve predominates in comparison with the restriction of orifice 98 by metering rod 80 to increase fuel flow to the engine for cold start enrichment, which is the desired effect.

I claim:

1. An internal combustion engine carburetor comprising a passage for air flow to the engine, a throttle disposed in said passage and rotatable between closed and open positions for controlling air flow therethrough, an air valve disposed in said passage upstream of said throttle and defining a controlled pressure region in said passage intermediate said air valve and said throttle, said air valve being rotatable between idle and open positions, means controlling said air valve to maintain a substantially constant pressure in said region whereby its rotative position is a measure of the rate of air flow through said passage, means connected to said air valve for supplying fuel to the engine at a rate proportional to the rotative displacement of said air valve from said idle position and inversely proportional to the pressure in said region, a lever secured to said air valve for rotation therewith through a predetermined path, a stop member disposed in said path for limiting closing movement of said air valve to establish said idle position, and means connected to said throttle and engageable with said stop member during movement of said throttle from said closed position for moving said stop member out of said air valve lever path whereby said air valve may be closed beyond said idle position to a closed position to decrease the pressure in said region and thereby increase the rate of fuel flow through said fuel supplying means.

2. A carburetor comprising an air inlet assembly having a metering region defined therein, a throttle valve disposed in said air inlet assembly posterior said metering region, said throttle rotatable between closed and fully open positions, an air valve disposed in said air inlet assembly anterior said metering region, said air valve rotatable between idle and open positions, means connected to said air valve for supplying fuel to said metering region, the rate of fuel flow through said means being inversely proportional to the pressure occurring in said region and further being directly proportional to the rotative position of said air valve; means controlling said air valve to maintain a substantially constant pressure in said region whereby its rotative position is a measure of the rate of air flow through said air inlet, said means including a housing member extending from said carburetor, a cover member adapted for registration with said housing, a diaphragm secured between and partitioning said housing and said cover member into an atmospheric chamber and a vacuum chamber, means exposing said vacuum chamber to the pressure occurring in said metering region and further exposing said atmospheric chamber to atmospheric pressure, and means connecting said diaphragm to said air valve for controlling the position of said air valve in response to pressure occurring in said metering region; cam means rotatably disposed on said carburetor, said cam means having a stop member extending therefrom for rotation through a predetermined path; means responsive to operating temperature and operatively connected to said cam for positioning said cam means; means disposed in the rotative path of said cam means and connected to said throttle for limiting the closure of said throttle; a lever extending from said air valve and disposed in the rotative path of said stop for engaging said stop and holding said air valve open at said idle position; and air valve release means comprising an outwardly extending pin secured to said cam and a canted spring having a flat portion operatively connected to said throttle and further having a bent portion and leading edge associated therewith and disposed in the rotative path of said pin; whereby said spring is adapted for registration with said pin so that as said throttle is closed said bent portion of said spring rides over said pin in a unidirectional ratcheting manner without resetting the position of said cam so that said stop may retain and hold said air valve open at said idle position, and as said throttle is opened said leading edge of said spring engages said pin and rotates said cam to disengage said stop from said air valve lever whereby said air valve may be closed beyond said idle position to a closed position to decrease the pressure in said region and thereby increase the rate of fuel flow through said fuel supplying means for cold start enrichment.

3. For an internal combustion engine, an air valve carburetor comprising an air inlet assembly for providing air flow to the engine, said air inlet assembly having a metering region, a shaft extending through and pivoted in said air inlet assembly posterior said metering region, a throttle valve secured to said shaft and rotatable between closed and fully open positions for controlling air flow through said air inlet, an air valve rotatably disposed in said air inlet assembly anterior said metering region, said air valve rotatable between idle and open positions, means connected to said air valve for supplying fuel to said metering region, the rate of fuel flow through said means being inversely responsive to the pressure in said region and further being directly responsive to the rotative position of said air valve, means controlling said air valve to maintain a substantially constant pressure in said region whereby its rotative position is a measure of the rate of air flow through said air inlet, said means including a housing member extending from said carburetor, a cover member adapted for registration with said housing, a diaphragm secured between and partitioning said housing and said cover member into an atmospheric chamber and a vac uum chamber, means exposing said vacuum chamber to the pressure occurring in said metering region and further exposing said atmospheric chamber to atmospheric pressure, means connecting said diaphragm to said air valve for positioning said air valve; means responsive to operating temperature, a cam member pivoted on said carburetor; means operatively connecting said cam to said temperature responsive means for positioning said cam in response to operating temperature; a fast idle lever secured to said shaft and having a tang portion disposed in the rotative path of said cam for engaging said cam thereby limiting the closure of said throttle; an adjustment screw threadedly carried in said tang portion; an auxiliary throttle lever pivoted on said shaft and having an abutment arm with a rounded end disposed in the path of said adjustment screw, a torsion spring wound around said shaft and engaging said auxiliary throttle and fast idle levers for biasing said abutment arm and said adjustment screw into interengagement; an air valve lever secured to said air valve for positioning said air valve, said air valve lever having a tang portion, an idle mixture adjusting screw threadedly carried in said tang portion, a link connected at one end to said auxiliary throttle lever and having another end disposed in a slot formed in said air valve lever for opening said air valve from said idle position only when said throttle is fully open; a stop member extending outwardly from said cam for engaging said idle mixture adjusting screw when said operating temperature is above a selected value, said stop thereby limiting the closure of said air valve at said idle position; a canted spring having a flat portion secured to said fast idle lever and further having a bent portion extending towards said cam and a leading edge associated therewith; and a pin secured to and extending from said cam and disposed in the rotative path of said leading edge and said bent portion; whereby said spring is adapted for registration with said pin so that as said throttle is closed said bent portion of said spring rides over said pin in a unidirectional ratcheting manner without resetting the position of said cam so that said stop may engage said idle mixture adjusting screw and support said air valve lever thereby holding said air valve open to said idle position, and as said throttle is opened said leading edge of said spring engages said pin and rotates said cam to disengage said arm from said idle mixture adjusting screw so that said air valve may be closed beyond said idle position to a closed position to decrease the pressure in said region and thereby in crease the rate of fuel flow through said fuel supplying means for cold start enrichment. 

1. An internal combustion engine carburetor comprising a passage for air flow to the engine, a throttle disposed in said passage and rotatable between closed and open positions for controlling air flow therethrough, an air valve disposed in said passage upstream of said throttle and defining a controlled pressure region in said passage intermediate said air valve and said throttle, saId air valve being rotatable between idle and open positions, means controlling said air valve to maintain a substantially constant pressure in said region whereby its rotative position is a measure of the rate of air flow through said passage, means connected to said air valve for supplying fuel to the engine at a rate proportional to the rotative displacement of said air valve from said idle position and inversely proportional to the pressure in said region, a lever secured to said air valve for rotation therewith through a predetermined path, a stop member disposed in said path for limiting closing movement of said air valve to establish said idle position, and means connected to said throttle and engageable with said stop member during movement of said throttle from said closed position for moving said stop member out of said air valve lever path whereby said air valve may be closed beyond said idle position to a closed position to decrease the pressure in said region and thereby increase the rate of fuel flow through said fuel supplying means.
 1. An internal combustion engine carburetor comprising a passage for air flow to the engine, a throttle disposed in said passage and rotatable between closed and open positions for controlling air flow therethrough, an air valve disposed in said passage upstream of said throttle and defining a controlled pressure region in said passage intermediate said air valve and said throttle, saId air valve being rotatable between idle and open positions, means controlling said air valve to maintain a substantially constant pressure in said region whereby its rotative position is a measure of the rate of air flow through said passage, means connected to said air valve for supplying fuel to the engine at a rate proportional to the rotative displacement of said air valve from said idle position and inversely proportional to the pressure in said region, a lever secured to said air valve for rotation therewith through a predetermined path, a stop member disposed in said path for limiting closing movement of said air valve to establish said idle position, and means connected to said throttle and engageable with said stop member during movement of said throttle from said closed position for moving said stop member out of said air valve lever path whereby said air valve may be closed beyond said idle position to a closed position to decrease the pressure in said region and thereby increase the rate of fuel flow through said fuel supplying means.
 2. A carburetor comprising an air inlet assembly having a metering region defined therein, a throttle valve disposed in said air inlet assembly posterior said metering region, said throttle rotatable between closed and fully open positions, an air valve disposed in said air inlet assembly anterior said metering region, said air valve rotatable between idle and open positions, means connected to said air valve for supplying fuel to said metering region, the rate of fuel flow through said means being inversely proportional to the pressure occurring in said region and further being directly proportional to the rotative position of said air valve; means controlling said air valve to maintain a substantially constant pressure in said region whereby its rotative position is a measure of the rate of air flow through said air inlet, said means including a housing member extending from said carburetor, a cover member adapted for registration with said housing, a diaphragm secured between and partitioning said housing and said cover member into an atmospheric chamber and a vacuum chamber, means exposing said vacuum chamber to the pressure occurring in said metering region and further exposing said atmospheric chamber to atmospheric pressure, and means connecting said diaphragm to said air valve for controlling the position of said air valve in response to pressure occurring in said metering region; cam means rotatably disposed on said carburetor, said cam means having a stop member extending therefrom for rotation through a predetermined path; means responsive to operating temperature and operatively connected to said cam for positioning said cam means; means disposed in the rotative path of said cam means and connected to said throttle for limiting the closure of said throttle; a lever extending from said air valve and disposed in the rotative path of said stop for engaging said stop and holding said air valve open at said idle position; and air valve release means comprising an outwardly extending pin secured to said cam and a canted spring having a flat portion operatively connected to said throttle and further having a bent portion and leading edge associated therewith and disposed in the rotative path of said pin; whereby said spring is adapted for registration with said pin so that as said throttle is closed said bent portion of said spring rides over said pin in a unidirectional ratcheting manner without resetting the position of said cam so that said stop may retain and hold said air valve open at said idle position, and as said throttle is opened said leading edge of said spring engages said pin and rotates said cam to disengage said stop from said air valve lever whereby said air valve may be closed beyond said idle position to a closed position to decrease the pressure in said region and thereby increase the rate of fuel flow through said fuel supplying means for cold start enrichment. 